Add 'alias_id' config option to disable top-level _id/id aliasing

[AymenReIn]

Summary

Adds a new alias_id connection config option (default: true) that allows disabling the automatic top-level _id ↔ id aliasing introduced in v5.0.

• When alias_id is false, root-level id is treated as a regular field and not converted to/from _id
• When alias_id is true (default), behavior is identical to current — zero breaking changes
• When disabling alias_id, also set rename_embedded_id_field to false to prevent compound query operators ($and/$or) from incorrectly aliasing root-level id fields in nested where clauses

Problem

Applications upgrading from v4 to v5 that have documents with a business id field (e.g., external API IDs, legacy system identifiers) alongside MongoDB's _id experience data corruption because the aliasing overwrites the custom id field with _id.

The existing rename_embedded_id_field config (v5.3+) only controls embedded document aliasing. There is currently no way to disable top-level aliasing, which has been reported in:

• Bug Report: Inability to Disable Top-Level _id Aliasing in Laravel MongoDB Package #3392 — Requesting reconsideration with this minimal, backward-compatible implementation
• Community forum: https://www.mongodb.com/community/forums/t/issue-with-id-to-id-conversion-when-upgrading-to-laravel-mongodb-v5-laravel-12-support/321882
• Community forum: https://www.mongodb.com/community/forums/t/id-vs-id-with-laravel-mongodb-v5/316408

Changes

File	Change
src/Connection.php	New aliasId property, getter/setter, config init ('alias_id' => true)
src/Query/Builder.php	compileWheres(): gate id → _id column rename on getAliasId()
src/Query/Builder.php	aliasIdForQuery(): separate root aliasing (alias_id) from embedded aliasing (rename_embedded_id_field)
src/Query/Builder.php	aliasIdForResult(): same separation for result processing
src/Eloquent/DocumentModel.php	getIdAttribute(): return actual id attribute without _id fallback when disabled
src/Eloquent/DocumentModel.php	getKeyName(): return _id as primary key when disabled
src/Eloquent/DocumentModel.php	getKey(): return raw _id attribute directly, bypassing accessor

Config usage

// config/database.php
'mongodb' => [
    'driver' => 'mongodb',
    'dsn' => env('MONGODB_URI'),
    'database' => env('MONGODB_DATABASE'),
    'alias_id' => false,
    'rename_embedded_id_field' => false,
],

Or at runtime:

DB::connection('mongodb')->setAliasId(false);
DB::connection('mongodb')->setRenameEmbeddedIdField(false);

Why both config keys?

The aliasIdForQuery() method recurses into nested arrays with root=false. Compound query operators like $and/$or (automatically added by SoftDeletes or multiple where() clauses) create nested array structures that are incorrectly treated as embedded documents during recursion. Setting rename_embedded_id_field to false prevents this from converting root-level id to _id inside these query structures.

Test plan

• All existing tests pass unchanged (default alias_id => true)
• Verified with integration tests: model lifecycle (create, refresh, query, update), query builder insert, raw MongoDB document verification, soft deletes with compound where clauses